The invention relates to a drive mechanism for an electric switch made up of at least one switching unit, in particular a circuit breaker or power switch, comprising a tensioning mechanism in the form of a transition point or overturn mechanism which can act upon the at least one switching unit, actuating means for tensioning the tensioning mechanism, drive means for driving the at least one switching unit under the influence of the energy stored in the tensioning mechanism, means for resetting the at least one switching unit from the driven state, and a coupling mechanism for bringing the tensioning mechanism in its tensioned state into engagement with the drive means, for driving the at least one switching unit, and for releasing the engagement of the tensioning mechanism and the drive means when the at least one switching unit is in the driven state.
A drive mechanism with a tensioning mechanism in the form of a transition point or overturn mechanism is known from Dutch Patent Application 8803018, in which the tensioning mechanism for driving the switching unit moves past its transition point or dead centre, thus in the same direction as that in which the tensioning mechanism is tensioned. When the switching unit is being driven or switched on, the drive means remain in engagement with the tensioning mechanism. For switching off the switching unit, this engagement first has to be released by means of the actuating means.
Although the switching unit can be switched on and off at a specific speed and in a reproducible manner with this known device, it is not possible when, for example, switched to a short-circuit current, to switch off the switching unit directly, i.e. without operating the actuating means.
A switch having a drive mechanism with a tensioning mechanism in the form of a transition point or overturn mechanism is also known from U.S. Pat. No. 4,336,520, which switch is also provided with a coupling mechanism. Said coupling mechanism ensures that the drive means for driving the switching unit are brought into engagement with the tensioning mechanism when it is tensioned, and that when the switching unit is being driven the engagement of the tensioning mechanism and the drive means is released.
During driving of the switching unit the tensioning mechanism, as in the case of the abovementioned Dutch Patent Application, moves past its transition point, thus in the same direction as that in which the tensioning mechanism is tensioned. For switching on the switch again after it has been switched off, such a tensioning mechanism must first be moved through the actuating means into a rest position suitable for switching on the switch. For switching on the switch, the maximum storage energy, i.e. the energy required for moving the tensioning mechanism past its transition point or dead centre, must always be supplied to the tensioning mechanism by the actuating means.
French Patent 808,888 also discloses a drive mechanism for an electric switch, provided with a tensioning mechanism in the form of a transition point or overturn mechanism, in which the drive means do not remain in engagement with the tensioning mechanism when the switching unit is being driven or is switched on. Here too, for switching on the switch again, the tensioning mechanism must be reset in a stable rest position by means of the actuating means, while the operation of the drive mechanism is again based on the tensioning mechanism moving past the transition point or dead centre.